Perry said that he did not know whether faulty cockpit equipment might be involved or whether the Iraqis were playing cat and mouse with their radar systems. An investigation was under way, he said.
In the meantime, allied flights over Iraq's southern no-fly zone will continue, Perry added, even though Saddam Hussein's forces have been ''quite quiet'' in the past week.
In separate incidents, the pilots of U.S. Air Force F-16s fired high-speed missiles when they got warning signals in their cockpits that they had been ''locked on'' by Iraqi surface-to-air missile sites, Pentagon officials said. The first such firing occurred early Saturday and the second yesterday.
Perry said he had no reports on possible damage caused by the missiles.
Iraq denied the missile firings occurred, characterizing the reports as a campaign ploy by the Clinton administration.
''Fabricating this false report is part of American-style electioneering,'' an Iraqi Foreign Ministry official was quoted yesterday by the official Iraqi News Agency. ''It seems that, for the second time, fabricators of this report have the urge to divert the attention of American voters from their domestic scandals by creating false problems abroad.''
Perry told reporters at the Pentagon that ''these incidents did occur.''
''In both cases, the F-16 warning gear alerted (the pilots) that they were being tracked by a surface-to-air missile system and ... they launched a HARM missile, a radiation-seeking missile, toward the source of that radiation.''
Even though it now appears that no Iraqi missiles were launched, both pilots acted appropriately. Their rules of engagement allow quick responses to potentially hostile acts, Perry said.
Asked whether Saddam's move to rebuild his air defenses caused him any worry, Perry responded, ''No.'' He said allied aircraft would continue to monitor the zone carefully.
''Saddam Hussein has a very clear warning already - the fact that we conduct 100 sorties a day over this area and we conduct them with airplanes that are very well armed and are quite capable of defending themselves,'' Perry said.
The latest firing occurred at 4 a.m. Ann Arbor time about 25 miles from where the earlier firing took place. Both occurred just south of the 32nd parallel, Perry said.
In both cases, the pilots returned safely to their base in Saudi Arabia.
White House spokesperson Mike McCurry said President Clinton was briefed on the missile firings and analysts were trying to ''determine why we've had a second incident.''
In a statement Sunday about the first incident, the Pentagon said ''subsequent analysis did not support the initial indications of radar activity'' on the part of the Iraqis.
Since the end of the Gulf War in 1991, the United States and its allies have maintained a no-fly zone over southern Iraq.
The U.S. missile firings were the first of their kind since Sept. 4, when Iraqi forces confronted U.S. flyers twice as they began their patrols over an expanded no-fly zone for Iraqi aircraft. Washington had unilaterally extended the zone the day before 60 miles northward to the 33rd parallel, taking it to the outskirts of Baghdad.
The administration argued that the extension reinforced the buffer zone between Iraq and its neighbors.
The confrontations over the no-fly zone followed two separate strikes by a total of 44 cruise missiles against 15 Iraqi air-defense sites. Those strikes against Iraqi air defense sites had been sparked by Saddam's attacks on the Kurds in the north.
Iraq said it remained committed to a decision it made in September not to fire on U.S. warplanes enforcing no-fly zones over southern and northern Iraq. Warplanes from France and Britain also patrol the zones.